It may come as a surprise that many plant materials are poisonous or toxic to honey bees. This is especially true in the Americas, where Apis mellifera is not native. Strictly speaking In fact, the honey bee is perhaps the first “invasive insect species” brought by humans to the New World. The insect has been around so long now, however, that it must be considered ubiquitous and practically indigenous.
Two southern U.S. plant species have been shown to damage honey bee colonies. Fortunately, these poisonous plants are in the minority and usually nectar flow or pollen production by them is not prolific enough to be considered a threat. However, at certain times, they can pose a real danger to honey bee colonies.
Carolina jessamine, (Gelsemium sempervirens), sometimes called yellow jessamine, is a woody vine which may grow to a height of forty feet and have a diameter of an inch or more. The plant occurs in hammocks and swamps from eastern Virginia to as far south as Highlands County, Florida just north of Lake Okeechobee. It may also be found as far west as Texas. The plant’s toxicity to bees comes as little surprise because large doses of extracts fed to other animals are known to be fatal.
The other plant, Summer Titi (Cyrilla racemiflora), American cyrilla or southern leatherwood, is found locally in west Florida and south Alabama. The common name is unfortunate, because it may cause confusion with the Spring Titi (Cliftonia monophylla) or buckwheat tree, which is considered an excellent honey plant in the same areas. The nectar and/or pollen of the summer titi is responsible for a condition called “purple brood.” The brood turns a deep blue and dies; larvae, pupae and newly emerged bees are all affected. The severity of purple brood appears to vary from year to year, depending on prevailing conditions. Other plants include mountain laurel, rhododendron, and California buckeye.
There are two courses of action open to the beekeeper faced with possible nectar sources that are harmful to bees. (1) avoid large tracts of these plants by moving bees away during the bloom, and (2) feed colonies sugar syrup when the plants are blooming to dilute the potential effects.
To determine if any plants might be a problem in a specific area, the best counsel is to ask about such possibilities at a local beekeepers’ meeting. Often this information is well known, but may provoke little discussion, especially when these plants are not in bloom.